The present invention relates to a pipe socket and a method of forming a pipe socket at the end portion of a thermoplastic material pipe.
A pipe joint between the end portions of plastic pipes is usually established by introducing a spigot end of one of the pipe end portions into a socket of the other pipe end portion, the sealing between the outer surface of the spigot end and the inner surface of the socket being provided by means of a sealing ring positioned in the annular space between said surfaces. Thereby, it is usual to locate the sealing ring in an inner groove in the socket. In pipes consisting of thermoplastic material, especially polyvinyl chloride, it is common to form the socket necessary for the pipe jointing by radially expanding the pipe wall in the region of the pipe end portion. This is usually conducted by heating the pipe end portion to a plastic condition, whereupon the pipe end portion thus being in softened state is radially expanded by means of a mandrel which is introduced into the pipe end portion. It is common practice to provide the pipe end portion in the same step of operation with an inner groove for receiving the sealing ring which is subsequently used for sealing the joint between the socket and the spigot end introduced therein.
According to a method recently developed the so called socketing operation for forming the socket at the pipe end portion and the positioning of the sealing ring in a locked-in position in the socket is conducted in one single step by positioning the sealing ring on the mandrel before the mandrel is introduced into the softened pipe end portion, whereupon the softened pipe end portion is moved along the outer surface of the mandrel as well as the sealing ring positioned thereon, the sealing ring being retained in the socket after the pipe end portion has been cooled and solidified and the mandrel has been withdrawn from the socket. Thus, the ring constitutes a mould element during the socketing operation and constitutes a sealing ring during a subsequent jointing operation.
In connection with certain thermoplastic materials the method of forming a pipe socket described above can not be used because of the fact that these plastic materials have insufficient shape permanence. Thus, in manufacturing sockets in polyethylene pipes it has been necessary to manufacture separate sockets by means of injection moulding and to connect the sockets with the end portions of the polyethylene pipes by means of welding or other connection methods.
The object of the invention is to provide a pipe socket and a method of forming such a pipe socket which can be used also in connection with pipes having inferior shape permanence and dimensional stability in connection with heating.
In order to comply with this object the pipe socket according to the invention comprises a sleeve defining the inner surface of the socket, an end portion of a thermoplastic material pipe moulded around the sleeve, an outer sealing ring positioned between the inner surface of the pipe end portion and the outer surface of the sleeve for sealing the pipe end portion and the sleeve in relation to each other and an inner sealing ring positioned at the inner surface of the sleeve for sealing the space between the inner surface of the pipe socket and the outer surface of a spigot end of a connecting pipe introduced into the socket, the pipe socket being characterized in that the outer sealing ring and the inner sealing ring are connected with each other.
In a preferred embodiment of the pipe socket according to the invention the sealing rings are chemically bound to the sleeve.
In accordance with the invention it is possible to provide a pipe socket by heating the end portion of the thermoplastic material pipe and moving the end portion over the sleeve while the end portion is expanded for providing the pipe socket which will then consist of the pipe end portion and said sleeve, the inner surface of the sleeve defining the inner surface of the pipe socket. Thereby the inferior shape permanence and dimensional stability of the termoplastic material of the pipe end portion are of no importance as the surface which is of importance with regard to the tightness of the pipe joint, namely the inner surface of the socket, is defined by the sleeve which is of good shape permanence and dimensional stability.
In a preferred embodiment of the pipe socket according to the invention the outer surface of the sleeve has a section of a larger diameter and a section positioned adjacent the free end of the pipe socket of less diameter, an annular surface positioned between said sections and extending transversely of the axis of the sleeve, the outer sealing ring being constituted by a sealing lip having a base portion which is connected with and is preferably chemically bound to the sleeve at said annular surface and is positioned in a space defined by said annular surface and by the inner surface of the pipe end portion and the section of the outer surface of the sleeve having less diameter.
In the method of forming a pipe socket according to the invention a pipe end portion is moulded around a sleeve which after the moulding operation is left in the pipe end portion for defining the inner surface of the socket, wherein the sleeve is in advance of the moulding of the pipe end portion around the sleeve provided with an outer sealing ring for sealing the pipe end portion and the sleeve in relation to each other and with an inner sealing ring connected with said outer sealing ring for sealing the space between the inner surface of the pipe socket and the outer surface of a spigot end of a connecting pipe introduced into the socket.